Liquid crystal display device

ABSTRACT

A liquid crystal display device includes a first liquid crystal display panel that displays a color image, a second liquid crystal display panel that displays a monochrome image, and a display controller that controls the display of the first liquid crystal display panel and the display of the second liquid crystal display panel. The display controller switches the display of the second liquid crystal display panel between a monochrome display that displays a monochrome image and an all-white display. In a state in which the display of the second liquid crystal display panel is the monochrome display, when a response time between predetermined gradations is greater than or equal to a predetermined first response time, the display controller switches the display of the second liquid crystal display panel from the monochrome display to the all-white display.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Japanese Patent Application No.2021-89503, filed on May 27, 2021, the entire disclosure of which isincorporated by reference herein.

FIELD

The present disclosure relates generally to a liquid crystal displaydevice.

BACKGROUND

In the related art, liquid crystal display devices are known in which aplurality of liquid crystal display panels are stacked to improvecontrast ratio. For example, International Publication No. WO2007/040139describes a liquid crystal display device including a color liquidcrystal panel positioned on an observer side and a black and whiteliquid crystal panel positioned on a side, opposite the surface of theobserver side, of the color liquid crystal panel.

With the liquid crystal display device of International Publication No.WO2007/040139, the transmittance is the product of the transmittances ofthe various liquid crystal display panels and, as such, thetransmittance of the liquid crystal display device decreases. However,using negative liquid crystal in a horizontal electric field type liquidcrystal display panel is known as a method for improving thetransmittance of the liquid crystal display panel. Unexamined JapanesePatent Application Publication No. 2003-15146 discloses that rises ofliquid crystal molecules can be suppressed and decreases in the maximumtransmittance can be suppressed by using negative liquid crystal in ahorizontal electric field type liquid crystal display panel.

The transmittance of a liquid crystal display device improves whenapplying the horizontal electric field type liquid crystal display panelthat uses negative liquid crystal of Unexamined Japanese PatentApplication Publication No. 2003-15146 to the liquid crystal displaydevice of International Publication No. WO2007/040139. However,typically, the response time of a liquid crystal display panel that usesnegative liquid crystal is longer than the response time of a liquidcrystal display panel that uses positive liquid crystal and, as such,deteriorations (display blurring, image tailing, and the like) indisplay quality are more likely to occur, particularly at lowtemperatures at which the response time is longer.

SUMMARY

A liquid crystal display device of the present disclosure includes:

a first liquid crystal display panel that displays a color image;

a second liquid crystal display panel that is positioned on a side,opposite a surface of an observer side, of the first liquid crystaldisplay panel so as to overlap the first liquid crystal display panel,and that displays a monochrome image; and

a display controller that controls a display of the first liquid crystaldisplay panel and a display of the second liquid crystal display panel,and that switches the display of the second liquid crystal display panelbetween a monochrome display that displays the monochrome image and anall-white display, wherein

a response time of the second liquid crystal display panel is longerthan a response time of the first liquid crystal display panel, and

in a state in which the display of the second liquid crystal displaypanel is the monochrome display, when a response time betweenpredetermined gradations is greater than or equal to a predeterminedfirst response time, the display controller switches the display of thesecond liquid crystal display panel from the monochrome display to theall-white display.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of this application can be obtained whenthe following detailed description is considered in conjunction with thefollowing drawings, in which:

FIG. 1 is a schematic drawing illustrating a liquid crystal displaydevice according to Embodiment 1;

FIG. 2 is a schematic drawing illustrating a cross-section of a firstliquid crystal display panel, a second liquid crystal display panel, anda back light according to Embodiment 1;

FIG. 3 is a schematic drawing illustrating an example of thecorrespondence between main pixels of the first liquid crystal displaypanel and main pixels of the second liquid crystal display panel;

FIG. 4 is a schematic drawing illustrating an example of thecorrespondence between the main pixels of the first liquid crystaldisplay panel and the main pixels of the second liquid crystal displaypanel;

FIG. 5 is a drawing illustrating an example of the dependence ontemperature of the maximum response time of the liquid crystal displaydevice according to Embodiment 1;

FIG. 6 is a block diagram illustrating the configuration of a displaycontroller according to Embodiment 1;

FIG. 7 is a drawing illustrating an example of the dependence ontemperature of the maximum response time of a liquid crystal displaydevice according to Embodiment 2;

FIG. 8 is a drawing illustrating an example of the relationship betweenthe brightness of the main pixels of a liquid crystal display device,and displays of a first liquid crystal display panel and a second liquidcrystal display panel according to Embodiment 3; and

FIG. 9 is a block diagram illustrating the configuration of a displaycontroller according to a modified example.

DETAILED DESCRIPTION

Hereinafter, a liquid crystal display device according to variousembodiments is described while referencing the drawings.

Embodiment 1

A liquid crystal display device 10 according to the present embodimentis described while referencing FIGS. 1 to 6 . The liquid crystal displaydevice 10 displays a color image by a hereinafter described first liquidcrystal display panel 100 that displays a color image and a secondliquid crystal display panel 200 that displays a monochrome image.

As illustrated in FIG. 1 , the liquid crystal display device 10 includesa panel section 50, a back light 300, and a display controller 400. Thepanel section 50 includes the first liquid crystal display panel 100 andthe second liquid crystal display panel 200. The first liquid crystaldisplay panel 100 displays a color image. The second liquid crystaldisplay panel 200 displays a monochrome image. The back light 300 is alight source that emits light on the first liquid crystal display panel100 and the second liquid crystal display panel 200. The displaycontroller 400 controls the displays of the first liquid crystal displaypanel 100 and the second liquid crystal display panel 200. Furthermore,the display controller 400 switches the display of the second liquidcrystal display panel 200 between a monochrome display and an all-whitedisplay. Herein, the term “monochrome display” refers to a display of amonochrome image, and the term “all-white display” refers to a displayin which the transmittance of all of the main pixels is maximized.

Panel Section

The panel section 50 includes the first liquid crystal display panel 100and the second liquid crystal display panel 200. The first liquidcrystal display panel 100 is positioned on an observer side and displaysa color image. The second liquid crystal display panel 200 is positionedon a side, opposite the surface of the observer side, of the firstliquid crystal display panel 100 (a back surface side of the firstliquid crystal display panel 100), and overlaps the first liquid crystaldisplay panel 100. The second liquid crystal display panel 200 displaysa monochrome image.

First Liquid Crystal Display Panel

The first liquid crystal display panel 100 is implemented as atransmissive horizontal electric field type liquid crystal display panelthat uses positive liquid crystal. The first liquid crystal displaypanel 100 is active matrix driven by thin film transistors (TFT).

The first liquid crystal display panel 100 includes main pixels arrangedin a matrix. The main pixels are formed from a red pixel that emits redlight, a green pixel that emits green light, and a blue pixel that emitsblue light (all not illustrated in the drawings). Note that, in thefollowing, the red pixel, the green pixel, and the blue pixel, aresometimes referred to collectively as sub pixels.

As illustrated in FIG. 2 , the first liquid crystal display panel 100includes a first TFT substrate 110, a first counter substrate 120, afirst liquid crystal 130, a first polarizing plate 132, a secondpolarizing plate 134, and a first driver circuit 136. The first TFTsubstrate 110 and the first counter substrate 120 sandwich the firstliquid crystal 130. The first polarizing plate 132 is provided on thefirst TFT substrate 110. The second polarizing plate 134 is provided onthe first counter substrate 120.

In one example, the first TFT substrate 110 is implemented as a glasssubstrate. TFTs for selecting sub pixels, a pair of electrodes forapplying voltage to the first liquid crystal 130, an alignment film foraligning the first liquid crystal 130, and the like are provided on amain surface 110 a on the first liquid crystal 130 side of the first TFTsubstrate 110 (all not illustrated in the drawings).

Furthermore, a plurality of common lines, a plurality of signal lines,and a plurality of scan lines are formed on the main surface 110 a ofthe first TFT substrate 110 (all not illustrated in the drawings). Thecommon lines supply common potential to one of the electrodes thatapplies voltage to the first liquid crystal 130. The signal linessupply, via the TFT, voltage to the other electrode that applies voltageto the first liquid crystal 130. The scan lines supply voltage foroperating the TFTs. The sub pixels are surrounded by the signal linesand the scan lines, and the TFTs are provided at the intersectionsbetween the scan lines and the signal lines.

The first polarizing plate 132 is provided on a main surface 110 b ofthe first TFT substrate 110, on the side opposite the main surface 110a.

The first counter substrate 120 faces the first TFT substrate 110 and isadhered to the first TFT substrate 110 by a seal material 138. In oneexample, the first counter substrate 120 is implemented as a glasssubstrate. A color filter layer 122, an alignment film that aligns thefirst liquid crystal 130, and the like are provided on a main surface120 a on the first liquid crystal 130 side of the first countersubstrate 120. In one example, the color filter layer 122 is implementedas a stripe-like color filter. Each of a red color filter, a green colorfilter, and a blue color filter of the color filter layer 122 issurrounded by a black matrix that blocks light, and corresponds to eachof the red pixel, the green pixel, and the blue pixel.

The second polarizing plate 134 is provided on a main surface 120 b ofthe first counter substrate 120, on the side opposite the main surface120 a.

The first liquid crystal 130 is sandwiched between the first TFTsubstrate 110 and the first counter substrate 120. The first liquidcrystal 130 is implemented as a positive-type nematic liquid crystal.The first liquid crystal 130 is aligned, by the alignment film, in adirection parallel to the main surface 110 a of the first TFT substrate110. Additionally, the first liquid crystal 130 rotates in a planeparallel to the main surface 110 a of the first TFT substrate 110 due tothe voltage applied from the electrodes.

The first polarizing plate 132 is provided on the main surface 110 b ofthe first TFT substrate 110. The second polarizing plate 134 is providedon the main surface 120 b of the first counter substrate 120. Thetransmittance axis of the first polarizing plate 132 and thetransmittance axis of the second polarizing plate 134 are arrangedparallel to an alignment direction of the first liquid crystal 130. Thefirst polarizing plate 132 is adhered to a fourth polarizing plate 234(described later) of the second liquid crystal display panel 200 by anadhesive layer 150.

The first driver circuit 136 is provided on the main surface 110 a ofthe first TFT substrate 110. The first driver circuit 136 supplies, onthe basis of a color image signal supplied from the display controller400, voltage to the scan lines, the signal lines, and the common lines.

Second Liquid Crystal Display Panel

As illustrated in FIG. 2 , the second liquid crystal display panel 200is positioned on the back surface side of the first liquid crystaldisplay panel 100. The second liquid crystal display panel 200 isadhered to the first liquid crystal display panel 100 by the adhesivelayer 150. The second liquid crystal display panel 200 displays amonochrome image. The response time of the second liquid crystal displaypanel 200 is longer than the response time of the first liquid crystaldisplay panel 100. Herein, the phrase “the response time is long” meansthat, when comparing response times between the same gradations, theresponse time between any of the gradations is long.

In the present embodiment, the second liquid crystal display panel 200is implemented as a transmissive horizontal electric field type liquidcrystal display panel that uses negative liquid crystal. The secondliquid crystal display panel 200 is active matrix driven by TFTs. Thesecond liquid crystal display panel 200 includes main pixels arranged ina matrix. The main pixels of the second liquid crystal display panel 200correspond to the main pixels of the first liquid crystal display panel100, and the main pixels of the liquid crystal display device 10 areformed from the main pixels of the first liquid crystal display panel100 and the main pixels of the second liquid crystal display panel 200.

More specifically, as illustrated in FIGS. 3 and 4 , one main pixel ofthe second liquid crystal display panel 200 corresponds to at least onemain pixel of the first liquid crystal display panel 100. Note that FIG.3 illustrates a configuration in which the main pixels of the secondliquid crystal display panel 200 correspond to the main pixels of thefirst liquid crystal display panel 100 on a one-to-one basis. FIG. 4illustrates a configuration in which one main pixel of the second liquidcrystal display panel 200 corresponds to a plurality of main pixels ofthe first liquid crystal display panel 100.

The second liquid crystal display panel 200 includes a second TFTsubstrate 210, a second counter substrate 220, a second liquid crystal230, a third polarizing plate 232, a fourth polarizing plate 234, and asecond driver circuit 236. The second TFT substrate 210 and the secondcounter substrate 220 sandwich the second liquid crystal 230. The thirdpolarizing plate 232 is provided on the second TFT substrate 210. Thefourth polarizing plate 234 is provided on the second counter substrate220. Note that the second liquid crystal display panel 200 does notinclude a color filter.

In one example, the second TFT substrate 210 is implemented as a glasssubstrate. As on the main surface 110 a of the first TFT substrate 110,TFTs for selecting main pixels, a pair of electrodes for applyingvoltage to the second liquid crystal 230, an alignment film for aligningthe second liquid crystal 230, common lines, signal lines, scan lines,and the like are provided on a main surface 210 a on the second liquidcrystal 230 side of the second TFT substrate 210 The configurations ofthe TFTs, the pair of electrodes, the common lines, and the like are thesame as the configurations of the TFTs, the pair of electrodes, thecommon lines, and the like of the first TFT substrate 110.

The third polarizing plate 232 is provided on a main surface 210 b ofthe second TFT substrate 210, on the side opposite the main surface 210a.

The second counter substrate 220 faces the second TFT substrate 210 andis adhered to the second TFT substrate 210 by a seal material 238. Inone example, the second counter substrate 220 is implemented as a glasssubstrate. A black matrix layer 222 that blocks light, an alignment filmthat aligns the second liquid crystal 230, and the like are provided ona main surface 210 a on the second liquid crystal 230 side of the secondcounter substrate 220. The black matrix layer 222 is provided in a gridpattern and defines the main pixels of the second liquid crystal displaypanel 200.

The fourth polarizing plate 234 is provided on a main surface 220 b ofthe second counter substrate 220, on the side opposite the main surface220 a.

The second liquid crystal 230 is sandwiched between the second TFTsubstrate 210 and the second counter substrate 220. The second liquidcrystal 230 is implemented as a negative-type nematic liquid crystal.The second liquid crystal 230 is aligned, by the alignment film, in adirection parallel to the main surface 210 a of the second TFT substrate210. Additionally, the second liquid crystal 230 rotates in a planeparallel to the main surface 210 a of the second TFT substrate 210 dueto the voltage applied from the electrodes.

The third polarizing plate 232 is provided on the main surface 210 b ofthe second TFT substrate 210. The fourth polarizing plate 234 isprovided on the main surface 220 b of the second counter substrate 220.The transmittance axis of the third polarizing plate 232 and thetransmittance axis of the fourth polarizing plate 234 are arrangedparallel to the alignment direction of the second liquid crystal 230.

The fourth polarizing plate 234 is adhered to the first polarizing plate132 of the first liquid crystal display panel 100 by the adhesive layer150. The transmittance axis of the fourth polarizing plate 234 and thetransmittance axis of the first polarizing plate 132 are arranged inparallel.

The second driver circuit 236 is provided on the main surface 210 a ofthe second TFT substrate 210. The second driver circuit 236 supplies, onthe basis of a signal supplied from the display controller 400, voltageto the scan lines, the signal lines, and the common lines.

Back Light

As illustrated in FIG. 2 , the back light 300 is arranged on the backsurface side of the second liquid crystal display panel 200. In oneexample, the back light 300 is implemented as a direct back light. Theback light 300 includes a white light emitting diode (LED), a reflectivesheet, a diffusion sheet, and the like (all not illustrated in thedrawings).

Display Controller

The display controller 400 controls the displays of the first liquidcrystal display panel 100 and the second liquid crystal display panel200. In a state in which the first liquid crystal display panel 100displays the color image and the display of the second liquid crystaldisplay panel 200 is the monochrome display, when a response timebetween predetermined gradations of the liquid crystal display device 10is greater than or equal to a predetermined first response time T1, thedisplay controller 400 switches the display of the second liquid crystaldisplay panel 200 from the monochrome display to the all-white display.Additionally, in a state in which the first liquid crystal display panel100 displays the color image and the display of the second liquidcrystal display panel 200 is the all-white display, when a response timebetween the predetermined gradations of the liquid crystal displaydevice 10 is less than a predetermined second response time T2, thedisplay controller 400 switches the display of the second liquid crystaldisplay panel 200 from the all-white display to the monochrome display.

The response time between the predetermined gradations and the firstresponse time T1 of the liquid crystal display device 10 are set on thebasis of in-vehicle standard related to display devices, thespecifications of the electronic device on which the liquid crystaldisplay device 10 is to be mounted, and the like. For example, when thein-vehicle standard related to display devices stipulates that thelongest response time between gradations at −20° C. be 180 ms or less,the response time between the predetermined gradations is set to thelongest response time between gradations. Additionally, the firstresponse time T1 is set to 180 ms. In the following, the longestresponse time between gradations is sometimes referred to as the“maximum response time.”

Furthermore, the second response time T2 of the liquid crystal displaydevice 10 refers to the response time in a state in which the firstliquid crystal display panel 100 displays the color image and thedisplay of the second liquid crystal display panel 200 is the all-whitedisplay, in a case in which the display of the second liquid crystaldisplay panel 200 is switched from the monochrome display to theall-white display at the first response time T1.

FIG. 5 illustrates an example of the dependence on temperature of themaximum response time of the liquid crystal display device 10. In oneexample, the display controller 400 switches the second liquid crystaldisplay panel 200 from the monochrome display to the all-white displaywhen the temperature of the panel section 50 decreases from 25° C. dueto a decrease in the ambient temperature, and the maximum response timeof the liquid crystal display device 10 is greater than or equal to thefirst response time T1 (180 ms). Due to this configuration, the maximumresponse time of the liquid crystal display device 10 becomes shorterthan the maximum response time in a case in which the second liquidcrystal display panel 200 maintains the monochrome display, anddeteriorations in display quality can be suppressed. Specifically, whena response time between the predetermined gradations of the liquidcrystal display device 10 is greater than or equal to the predeterminedfirst response time T1, the display controller 400 switches the displayof the second liquid crystal display panel 200, for which the responsetime is long, from the monochrome display to the all-white display. As aresult, even at low temperatures, it is possible to suppress theresponse time of the liquid crystal display device 10 from becominglonger, and deteriorations in display quality can be suppressed.

Meanwhile, the display controller 400 switches the second liquid crystaldisplay panel 200 from the all-white display to the monochrome displaywhen the temperature of the panel section 50 increases from the lowtemperature side (for example −25° C.) due to an increase in the ambienttemperature, and the maximum response time of the liquid crystal displaydevice 10 is shorter than the second response time T2 (85 ms in FIG. 3). Due to this configuration, the liquid crystal display device 10 candisplay color images that have higher contrast.

Next, the specific configuration of the display controller 400 isdescribed. As illustrated in FIG. 6 , the display controller 400includes an image data distributor 410, a response time measurer 420, acontrol signal generator 430, a first image signal generator 440, asecond image brightness signal generator 450, and a second image signalgenerator 460. The image data distributor 410 distributes input imagedata to the first image signal generator 440 and the second imagebrightness signal generator 450. The response time measurer 420calculates the response time between predetermined gradations of theliquid crystal display device 10. The control signal generator 430selects the display of the second liquid crystal display panel 200, andsends a control signal expressing the selected display to the firstimage signal generator 440 and the second image signal generator 460.

The first image signal generator 440 includes a first gradationconverter 441 and generates a color image to be displayed on the firstliquid crystal display panel 100. Additionally, the first image signalgenerator 440 sends a color image signal expressing the generated colorimage to the first liquid crystal display panel 100. The second imagebrightness signal generator 450 generates, from the input image data, abrightness signal for generating a monochrome image to be displayed onthe second liquid crystal display panel 200. The second image signalgenerator 460 generates, on the basis of the brightness signal sent fromthe second image brightness signal generator 450, the monochrome imageto be displayed on the second liquid crystal display panel 200, andsends a monochrome image signal expressing the generated monochromeimage to the second liquid crystal display panel 200. Additionally, thesecond image signal generator 460 generates a signal for setting thesecond liquid crystal display panel 200 to the all-white display, andsends the generated signal to the second liquid crystal display panel200. The second image signal generator 460 includes a calculator 461 anda second gradation converter 462.

In the following, the color image signal expressing the color image tobe displayed on the first liquid crystal display panel 100 is sometimesdescribed as a “color image signal.” Additionally, the monochrome imagesignal expressing the monochrome image to be displayed on the secondliquid crystal display panel 200 is sometimes described as a “monochromeimage signal”, and the signal for setting the second liquid crystaldisplay panel 200 to the all-white display is sometimes described as an“all-white display signal.”

The image data distributor 410 distributes input image data, input fromoutside, to the first image signal generator 440 and the second imagebrightness signal generator 450.

The response time measurer 420 calculates the response time betweenpredetermined gradations of the liquid crystal display device 10 fromchanges in a light amount of the liquid crystal display device 10measured by a photosensor 422, and a clock number. As illustrated inFIG. 2 , the photosensor 422 is provided on the second polarizing plate134 of the first liquid crystal display panel 100. The response timemeasurer 420 sends a signal expressing the response time betweenpredetermined gradations to the control signal generator 430.

The control signal generator 430 selects, on the basis of the responsetime between the predetermined gradations calculated by the responsetime measurer 420, the display of the second liquid crystal displaypanel 200 from among the monochrome display and the all-white display.

Specifically, in a state in which the first liquid crystal display panel100 displays the color image and the display of the second liquidcrystal display panel 200 is the monochrome display, when the responsetime between the predetermined gradations is greater than or equal tothe predetermined first response time T1, the control signal generator430 selects the all-white display as the display of the second liquidcrystal display panel 200. As a result, the display of the second liquidcrystal display panel 200 is switched from the monochrome display to theall-white display.

Meanwhile, in a state in which the first liquid crystal display panel100 displays the color image and the display of the second liquidcrystal display panel 200 is the monochrome display, when the responsetime between the predetermined gradations is shorter than thepredetermined first response time T1, the control signal generator 430selects the monochrome display as the display of the second liquidcrystal display panel 200. As a result, the display of the second liquidcrystal display panel 200 is maintained as the monochrome display.

Additionally, in a state in which the first liquid crystal display panel100 displays the color image and the display of the second liquidcrystal display panel 200 is the all-white display, when the responsetime between the predetermined gradations is shorter than thepredetermined second response time T2, the control signal generator 430selects the monochrome display as the display of the second liquidcrystal display panel 200. As a result, the display of the second liquidcrystal display panel 200 is switched from the all-white display to themonochrome display.

Meanwhile, in a state in which the first liquid crystal display panel100 displays the color image and the display of the second liquidcrystal display panel 200 is the all-white display, when the responsetime between the predetermined gradations is longer than thepredetermined second response time T2, the control signal generator 430selects the all-white display as the display of the second liquidcrystal display panel 200. As a result, the display of the second liquidcrystal display panel 200 is maintained as the all-white display.

The control signal generator 430 sends a control signal expressing theselected display to the first image signal generator 440 and the secondimage signal generator 460.

The first image signal generator 440 generates, from the input imagedata distributed by the image data distributor 410, a color image to bedisplayed on the first liquid crystal display panel 100. Specifically,the first gradation converter 441 of the first image signal generator440 performs gradation conversion for converting the distributed inputimage data to color image data having brightness-gradationcharacteristics suited to the first liquid crystal display panel 100. Inone example, a lookup table in which input/output relationships arepreset is used in the conversion of the data.

The first image signal generator 440 sends a color image signalexpressing the generated color image to the first driver circuit 136 ofthe first liquid crystal display panel 100.

When the control signal generator 430 selects the all-white display asthe display of the second liquid crystal display panel 200, it ispreferable that the first image signal generator 440 performs gammacorrection on the color image signal. For example, in the state in whichthe first liquid crystal display panel 100 displays the color image andthe display of the second liquid crystal display panel 200 is themonochrome display, when a gamma value of the liquid crystal displaydevice 10 is set to 2.2 (the gamma value of the first liquid crystaldisplay panel 100 is set to 1.1, and the gamma value of the secondliquid crystal display panel 200 is set to 1.1), the gamma value of theliquid crystal display device 10 becomes 1.1 when the display of thesecond liquid crystal display panel 200 is set to the all-white displayand the observer is more likely to feel uncomfortable with the displayof the liquid crystal display device 10. Therefore, it is particularlypreferable that the first image signal generator 440 performs gammacorrection for matching gamma characteristics (first gammacharacteristics) of the liquid crystal display device 10 in a state inwhich the display of the second liquid crystal display panel 200 is themonochrome display and gamma characteristics (second gammacharacteristics) of the liquid crystal display device 10 in a state inwhich the display of the second liquid crystal display panel 200 is theall-white display.

The second image brightness signal generator 450 generates a brightnesssignal for generating a monochrome image from the input image data. Asillustrated in FIGS. 3 and 4 , the main pixels of the second liquidcrystal display panel 200 that display the monochrome image correspondto one or more main pixels of the first liquid crystal display panel 100that displays the color image. In other words, the total number of mainpixels of the second liquid crystal display panel 200 is less than orequal to the total number of main pixels of the first liquid crystaldisplay panel 100. Accordingly, a brightness level of one main pixel ofthe second liquid crystal display panel 200 must be calculated on thebasis of the color image data of one or a plurality of main pixels ofthe first liquid crystal display panel 100 that correspond to that mainpixel.

As illustrated in FIG. 3 , when one main pixel of the first liquidcrystal display panel 100 that displays the color image corresponds toone main pixel of the second liquid crystal display panel 200 thatdisplays the monochrome image, the brightness level of the correspondingone main pixel of the second liquid crystal display panel 200 iscalculated on the basis of the color image data of the one main pixel ofthe first liquid crystal display panel 100. Additionally, as anothermethod, the brightness level of the monochrome image may be calculatedwith the maximum gradation value among a red gradation value, a greengradation value, and a blue gradation value of each main pixel of theinput image data as the brightness level of each main pixel of thesecond liquid crystal display panel 200.

As illustrated in FIG. 4 , when one main pixel of the second liquidcrystal display panel 200 that displays the monochrome image correspondsto a plurality of main pixels of the first liquid crystal display panel100 that displays the color image, the brightness level of the mainpixel of the second liquid crystal display panel 200 is calculated fromthe average value, the frequency value, the minimum value, the maximumvalue, and the like of the red gradation value, the green gradationvalue, and the blue gradation value of each main pixel of the firstliquid crystal display panel 100. The calculated brightness level may bea gradation value, for example.

The second image brightness signal generator 450 sends a brightnesssignal expressing the calculated brightness level to the second imagesignal generator 460.

When the control signal generator 430 selects the monochrome display asthe display of the second liquid crystal display panel 200, the secondimage signal generator 460 generates, on the basis of the brightnesssignal sent from the second image brightness signal generator 450, themonochrome image to be displayed on the second liquid crystal displaypanel 200. Additionally, when the control signal generator 430 selectsthe all-white display as the display of the second liquid crystaldisplay panel 200, the second image signal generator 460 generates asignal (all-white display signal) for setting the display of the secondliquid crystal display panel 200 to the all-white display. The secondimage signal generator 460 sends, to the second driver circuit 236 ofthe second liquid crystal display panel 200, a signal expressing themonochrome image (monochrome image signal) or the all-white displaysignal.

The second image signal generator 460 generates a monochrome image thathas been subjected to averaging processing and gradation conversion. Inone example, the calculator 461 of the second image signal generator 460uses a weighted average based on the distance from a target main pixelto average the brightness levels of the main pixels located within apredetermined distance from the target main pixel. Due to this, thesecond image signal generator 460 can generate a monochrome image thathas blurred edges. Furthermore, the second gradation converter 462 ofthe second image signal generator 460 generates monochrome image datahaving brightness-gradation characteristics suited to the second liquidcrystal display panel 200. The configuration of the second gradationconverter 462 is the same as that of the first gradation converter 441of the first image signal generator 440.

The monochrome image signal sent to the second liquid crystal displaypanel 200 is delayed, by the calculation of the brightness level, theaveraging processing, and the like executed by the second imagebrightness signal generator 450, with respect to the color image signalsent to the first liquid crystal display panel 100. As such, the displaycontroller 400 includes a non-illustrated synchronization circuit forsynchronizing the outputting of the monochrome image signal and thecolor image signal. Due to this synchronization circuit, the monochromeimage corresponding to the color image of the first liquid crystaldisplay panel 100 is displayed on the second liquid crystal displaypanel 200 and, as such, an appropriate color image is displayed on theliquid crystal display device 10.

The display controller 400 is configured from a central processing unit(CPU), a memory, and the like. In one example, the CPU executes programsstored in the memory to realize the functions of the display controller400.

As described above, when a response time between the predeterminedgradations of the liquid crystal display device 10 is greater than orequal to the predetermined first response time T1, the displaycontroller 400 switches the display of the second liquid crystal displaypanel 200 for which the response time is long from the monochromedisplay to the all-white display. As a result, the liquid crystaldisplay device 10 can suppress deteriorations in display quality.Additionally, when a response time between the predetermined gradationsof the liquid crystal display device 10 is shorter than the secondresponse time T2, the display controller 400 switches the second liquidcrystal display panel 200 from the all-white display to the monochromedisplay. As a result, the liquid crystal display device 10 can display acolor image that has high contrast and high display quality.

Embodiment 2

In Embodiment 1, when a response time between the predeterminedgradations of the liquid crystal display device 10 is shorter than thesecond response time T2, the display controller 400 switches the secondliquid crystal display panel 200 from the all-white display to themonochrome display. A configuration is possible in which the responsetime at which the second liquid crystal display panel 200 is switchedfrom the all-white display to the monochrome display is a response timethat is shorter than a third response time T3. The third response timeT3 is a response time that is a predetermined amount of time Td shorterthan the second response time T2. The other configurations of the liquidcrystal display device 10 of the present embodiment are the same as inEmbodiment 1 and, as such, the third response time T3 and the amount oftime Td are described.

Firstly, the switching of the display of the second liquid crystaldisplay panel 200 in Embodiment 1 is described. The second response timeT2 is the response time in a state in which the first liquid crystaldisplay panel 100 displays the color image and the display of the secondliquid crystal display panel 200 is the all-white display, in a case inwhich the display of the second liquid crystal display panel 200 isswitched from the monochrome display to the all-white display at thefirst response time T1. Accordingly, as illustrated in FIG. 5 , thetemperature of the panel section 50 at which the response time of theliquid crystal display device 10 is the first response time T1 issubstantially equivalent to the temperature of the panel section 50 atwhich the response time of the liquid crystal display device 10 is thesecond response time T2. In this case, when the temperature of the panelsection 50 fluctuates near the temperature at which the response time ofthe liquid crystal display device 10 is the first response time T1 orthe second response time T2, switching of the display of the secondliquid crystal display panel 200 may occur frequently. When switching ofthe display of the second liquid crystal display panel 200 occursfrequently, the observer has difficulty viewing the display.

Therefore, in the present embodiment, the response time at which thesecond liquid crystal display panel 200 is switched from the all-whitedisplay to the monochrome display is set to the third response time T3that is the predetermined amount of time Td shorter than the secondresponse time T2. The third response time T3 is set on the basis of thedependency on temperature of the response time of the liquid crystaldisplay device 10 in a state in which the display of the second liquidcrystal display panel 200 is set to the monochrome display, thedependency on temperature of the response time of the liquid crystaldisplay device 10 in a state in which the display of the second liquidcrystal display panel 200 is set to the all-white display, thein-vehicle standard related to display devices, the specifications ofthe electronic device on which the liquid crystal display device 10 isto be mounted, and the like.

In the present embodiment, as illustrated in FIG. 7 , the third responsetime T3 is set to a response time (54 ms in FIG. 7 ) at which theresponse time of the liquid crystal display device 10 is 100 ms in acase in which the display of the second liquid crystal display panel 200is switched from the all-white display to the monochrome display at thethird response time T3. In this case, the amount of time Td is set to 31ms (T2−T3=31). That is, in the present embodiment, the displaycontroller 400 switches the second liquid crystal display panel 200 fromthe all-white display to the monochrome display when the temperature ofthe panel section 50 increases from the low temperature side (forexample −25° C.) due to an increase in the ambient temperature, and themaximum response time of the liquid crystal display device 10 is shorterthan the third response time T3 (54 ms). Additionally, as in Embodiment1, the display controller 400 switches the second liquid crystal displaypanel 200 from the monochrome display to the all-white display when thetemperature of the panel section 50 decreases from 25° C. due to adecrease in the ambient temperature, and the maximum response time ofthe liquid crystal display device 10 is greater than or equal to thefirst response time T1 (180 ms).

In the present embodiment, as illustrated in FIG. 7 , the temperature ofthe panel section 50 at which the maximum response time of the liquidcrystal display device 10 is the third response time T3 is −5° C., andthe temperature at which the maximum response time of the liquid crystaldisplay device 10 is the first response time T1 is −13° C. As such, evenwhen the temperature of the panel section 50 fluctuates near thetemperature at which the response time of the liquid crystal displaydevice 10 is the first response time T1 or the third response time T3,the possibility of the display of the second liquid crystal displaypanel 200 switching frequently is small. Therefore, the liquid crystaldisplay device 10 of the present embodiment can realize stabledisplaying.

As described above, in the present embodiment, the response time atwhich the second liquid crystal display panel 200 is switched from theall-white display to the monochrome display is set to the third responsetime T3 that is the predetermined amount of time Td shorter than thesecond response time T2. As such, it is possible to suppress the numberof time the display of the second liquid crystal display panel 200 isswitched, and realize stable displaying of the liquid crystal displaydevice 10. Additionally, as with the liquid crystal display device 10 ofEmbodiment 1, the liquid crystal display device 10 of the presentembodiment can suppress deteriorations in display quality.

Embodiment 3

In Embodiment 1 and Embodiment 2, the liquid crystal display device 10switches the display of the second liquid crystal display panel 200directly between the monochrome display and the all-white display. Aconfiguration is possible in which, when switching the display of thesecond liquid crystal display panel 200 from the monochrome display tothe all-white display, between the monochrome display and the all-whitedisplay, the liquid crystal display device 10 displays, on the secondliquid crystal display panel 200, an image having a gradation between agradation of the monochrome display and the all-white display, themonochrome display being displayed on the second liquid crystal displaypanel immediately before switching to the all-white display.

In the present embodiment, when switching the display of the secondliquid crystal display panel 200 from the monochrome display to theall-white display, the display controller 400 generates an image(hereinafter referred to as “intermediate gradation image”) having agradation between a monochrome image being displayed on the secondliquid crystal display panel 200 immediately before switching to theall-white display and the all-white display. Additionally, the displaycontroller 400 of the present embodiment displays the generatedintermediate gradation image on the second liquid crystal display panel200, between the monochrome display and the all-white display of thesecond liquid crystal display panel 200. The other configurations of theliquid crystal display device 10 of the present embodiment are the sameas in Embodiment 1 or Embodiment 2 and, as such, the intermediategradation image is described.

At least one intermediate gradation image is generated by the secondimage signal generator 460 of the display controller 400. When switchingthe display of the second liquid crystal display panel 200 from themonochrome display to the all-white display, the second image signalgenerator 460 of the present embodiment generates the intermediategradation image on the basis of the brightness (gradation) immediatelybefore switching to the all-white display and the brightness (gradation)immediately after switching to the all-white display of each of the mainpixels of the liquid crystal display device 10.

FIG. 8 illustrates an example of the relationship between the brightnessof the main pixels of the liquid crystal display device 10 and thedisplays of the first liquid crystal display panel 100 and the secondliquid crystal display panel 200. As illustrated in FIG. 8 , whencomparing the state in which the display of the second liquid crystaldisplay panel 200 is the monochrome display and the state in which thedisplay of the second liquid crystal display panel 200 is the all-whitedisplay, the brightness of the main pixels is higher in the state inwhich the display of the second liquid crystal display panel 200 is theall-white display (except in cases in which the main pixels in themonochrome display are white).

In one example, the second image signal generator 460 of the presentembodiment sets the number of intermediate gradation images (in FIG. 8 ,there are four intermediate gradation images A to D) on the basis of themaximum difference among the differences between the brightnesses ofeach main pixel immediately before and after switching to the all-whitedisplay. Additionally, the second image signal generator 460 of thepresent embodiment sequentially generates a plurality of intermediategradation images (the intermediate gradation images A to D) such thatthe brightness of each main pixel gradually increases. The displaycontroller 400 sequentially outputs signals expressing the generatedintermediate gradation images (the intermediate gradation images A to D)to the second liquid crystal display panel 200, between the monochromedisplay and the all-white display. As a result, when switching thedisplay of the second liquid crystal display panel 200 from themonochrome display to the all-white display, the brightness of the mainpixels of the liquid crystal display device 10 increases gradually and,as such, the observer is less likely to feel discomfort due to theswitching of the display of the second liquid crystal display panel 200.Note that, it is not necessary to increase the brightness gradually formain pixels in which the difference between the brightnesses of the mainpixel immediately before and immediately after switching to theall-white display is small.

As described above, when switching the display of the second liquidcrystal display panel 200 from the monochrome display to the all-whitedisplay, the liquid crystal display device 10 of the present embodimentdisplays an image having a gradation between a gradation of themonochrome image being displayed on the second liquid crystal displaypanel 200 immediately before switching to the all-white display and theall-white display. As such, it is possible to suppress discomfort of theobserver caused by the switching of the display of the second liquidcrystal display panel 200. Additionally, as with the liquid crystaldisplay device 10 of Embodiment 1, the liquid crystal display device 10of the present embodiment can suppress deteriorations in displayquality.

MODIFIED EXAMPLES

Embodiments have been described, but various modifications can be madeto the present disclosure without departing from the spirit and scope ofthe present disclosure.

For example, in Embodiment 1, the first liquid crystal display panel 100is implemented as a horizontal electric field type liquid crystaldisplay panel that uses positive liquid crystal and the second liquidcrystal display panel 200 is implemented as a horizontal electric fieldtype liquid crystal display panel that uses negative liquid crystal, butthe type, liquid crystal, and the like of the first liquid crystaldisplay panel 100 and the second liquid crystal display panel 200 arenot limited thereto. A configuration is possible in which the type ofthe first liquid crystal display panel 100 and the second liquid crystaldisplay panel 200 is a vertical alignment (VA) mode, a twisted nematic(TN) mode, or the like.

A configuration is possible in which the first liquid crystal displaypanel 100 and the second liquid crystal display panel 200 areimplemented as horizontal electric field type liquid crystal displaypanels that use positive liquid crystal. Since one main pixel of thesecond liquid crystal display panel 200 corresponds to at least one mainpixel of the first liquid crystal display panel 100, the size of a mainpixel of the second liquid crystal display panel 200 is the same as thesize of a main pixel of the first liquid crystal display panel 100 ormultiple times the size of a main pixel of the first liquid crystaldisplay panel 100. When the size of a main pixel of the second liquidcrystal display panel 200 is multiple times the size of a main pixel ofthe first liquid crystal display panel 100, the aperture ratio of themain pixel of the second liquid crystal display panel 200 increases andthe degree of freedom related to pixel design increases and, as aresult, the transmittance of the second liquid crystal display panel 200can be further increased. Furthermore, the permittivity in the moleculeminor axis direction of the second liquid crystal 230 used in the secondliquid crystal display panel 200 is preferably greater, and is morepreferably 10% or more greater, than the permittivity in the moleculeminor axis direction of the first liquid crystal 130 used in the firstliquid crystal display panel 100. As a result, it is possible tosuppress rises of the liquid crystal molecules in the second liquidcrystal display panel 200 and improve the transmittance of the secondliquid crystal display panel 200. The second liquid crystal displaypanel 200 does not include sub pixels and is not provided with a colorfilter and, as such, the transmittance of the main pixels is easier toimprove. Moreover, by increasing the permittivity in the molecule minoraxis direction of the second liquid crystal 230 and improving thetransmittance of the second liquid crystal display panel 200, it ispossible to more effectively improve the transmittance of the firstliquid crystal display panel 100.

In Embodiment 1, the response time measurer 420 calculates the responsetime between predetermined gradations from changes in the light amountof the liquid crystal display device 10 measured by the photosensor 422.As illustrated in FIG. 9 , a configuration is possible in which thedisplay controller 400 includes a temperature-response time converter520 instead of the response time measurer 420, and thetemperature-response time converter 520 calculates the response timebetween predetermined gradations from a temperature measured by atemperature sensor 522 provided in the panel section 50. In such a case,the temperature-response time converter 520 calculates the response timebetween predetermined gradations from the temperature measured by thetemperature sensor 522, and the relationship between the temperature ofthe panel section 50 and the response time between predeterminedgradations. The relationship between the temperature of the panelsection 50 and the response time between predetermined gradations ismeasured in advance.

A configuration is possible in which the panel section 50 of the liquidcrystal display device 10 of Embodiments 1 to 3 includes a heatingheater. With such a configuration, even when the ambient temperaturedecreases, it is possible to suppress lengthening of the response timeof the liquid crystal display device 10, and further suppressdeteriorations in display quality of the liquid crystal display device10.

The foregoing describes some example embodiments for explanatorypurposes. Although the foregoing discussion has presented specificembodiments, persons skilled in the art will recognize that changes maybe made in form and detail without departing from the broader spirit andscope of the invention. Accordingly, the specification and drawings areto be regarded in an illustrative rather than a restrictive sense. Thisdetailed description, therefore, is not to be taken in a limiting sense,and the scope of the invention is defined only by the included claims,along with the full range of equivalents to which such claims areentitled.

What is claimed is:
 1. A liquid crystal display device, comprising: afirst liquid crystal display panel that displays a color image; a secondliquid crystal display panel that is positioned on a side, opposite asurface of an observer side, of the first liquid crystal display panelso as to overlap the first liquid crystal display panel, and thatdisplays a monochrome image; and a display controller that controls adisplay of the first liquid crystal display panel and a display of thesecond liquid crystal display panel, and that switches the display ofthe second liquid crystal display panel between the monochrome image andan all-white image, wherein a response time of the second liquid crystaldisplay panel is longer than a response time of the first liquid crystaldisplay panel, and in a state in which the second liquid crystal displaypanel is displaying the monochrome image, when a response time betweenpredetermined gradations is greater than or equal to a predeterminedfirst response time, the display controller switches the display of thesecond liquid crystal display panel from the monochrome image to theall-white image.
 2. The liquid crystal display device according to claim1, wherein when a response time between the predetermined gradations isshorter than a second response time in a state in which the secondliquid crystal display panel displays the all-white image, the secondresponse time being a response time between the predetermined gradationsin a state in which, when the second liquid crystal display panel isswitched to display the all-white image at the first response time, thedisplay of the second liquid crystal display panel is the all-whiteimage, the display controller switches the display of the second liquidcrystal display panel from the all-white image to the monochrome image.3. The liquid crystal display device according to claim 2, wherein inthe state in which the display of the second liquid crystal displaypanel is the all-white image, when a response time between thepredetermined gradations is shorter than a third response time that is apredetermined amount of time shorter than the second response time, thedisplay controller switches the display of the second liquid crystaldisplay panel from the all-white image to the monochrome image.
 4. Theliquid crystal display device according to claim 1, wherein when thedisplay of the second liquid crystal display panel is the all-whiteimage, the display controller performs gamma correction on a color imagesignal to be input into the first liquid crystal display panel.
 5. Theliquid crystal display device according to claim 4, wherein the gammacorrection matches first gamma characteristics in a state in which thedisplay of the second liquid crystal display panel is the monochromeimage to second gamma characteristics in a state in which the display ofthe second liquid crystal display panel is the all-white image.
 6. Theliquid crystal display device according to claim 1, wherein whenswitching the display of the second liquid crystal display panel fromthe monochrome image to the all-white image, between the monochromeimage and the all-white image, the display controller displays, on thesecond liquid crystal display panel, an image having a gradation betweena gradation of the monochrome image being displayed on the second liquidcrystal display panel immediately before switching to the all-whiteimage and the all-white image.
 7. The liquid crystal display deviceaccording to claim 1, wherein the first liquid crystal display panel andthe second liquid crystal display panel are horizontal electric fieldtype liquid crystal display panels, the first liquid crystal displaypanel includes a positive first liquid crystal, the second liquidcrystal display panel includes a positive second liquid crystal, andpermittivity in a molecule minor axis direction of the second liquidcrystal is greater than permittivity in a molecule minor axis directionof the first liquid crystal.